(1) Field of the Invention
The present invention relates to a preheater assembly, to a cylinder head fitted with the assembly, to a piston engine fitted with such a cylinder head, and to an aircraft.
The invention thus lies in the narrow technical field of preheater devices for a piston engine, and in particular a diesel engine. More particularly, the invention is situated in the technical field of aircraft having a piston engine with compression ignition.
(2) Description of Related Art
In particular, an aircraft may have at least one rotor for providing it with at least part of its lift and/or its propulsion. The rotor is then driven in rotation by a power plant comprising at least one engine. The engine may be a piston engine.
A piston engine usually comprises an engine block with one cylinder per piston, each piston sliding in a respective cylinder. Each cylinder is then closed by a cylinder head.
Furthermore, the operation of a diesel engine relies on self-ignition of a fuel in a combustion chamber filled with compressed air at a high temperature. Consequently, the air must reach a minimum temperature at the end of compression in order to cause the fuel to ignite.
Unfortunately, this minimum temperature can be difficult to reach when the engine is cold.
Consequently, a diesel engine may include a preheater system.
Heater systems using water seek to heat the entire engine.
Such systems are advantageous, but arranging them in an aircraft is difficult.
Other heater systems seek to heat the gas prior to admitting it into a combustion chamber.
Another system consists in using one glowplug per cylinder.
A glowplug comprises in succession: a connection terminal; a body; and then a heater tip. A heater filament is included in the tip and is connected to the connection terminal.
Under such circumstances, the glowplug passes through the cylinder head in order to lead into the combustion chamber. The body of the glowplug thus possesses a thread that is screwed into a thread of the cylinder head. The body also has a conical bearing surface that becomes pressed against a conical seat in the cylinder head in order to guarantee that the assembly is leaktight.
Under such circumstances, the heater tip is advantageously positioned at least in part in the combustion chamber so as to have the stream of fuel that is injected into the combustion chamber impact thereagainst.
An electric current is then applied to the connection terminal in order to heat the tip of the glowplug by means of the heater filament. The tip creates a hot point in the combustion chamber that enables the mixture of air and fuel to ignite. Consequently, the glowplug enables a diesel piston engine to be started when cold.
The use of a glowplug avoids arranging a heater system that is complex and bulky.
Nevertheless, a cylinder head is also provided with admission and exhaust valves and with fuel injectors.
Consequently, the space available for arranging a glowplug can be restricted.
The positioning of the thread of a given glowplug can make it difficult to arrange in a cylinder head.
Consequently, arranging an existing glowplug on a new cylinder head can turn out to be difficult.
A manufacturer can then envisage developing a new glowplug adapted to the new cylinder head. Nevertheless, developing a new glowplug is particularly expensive. Such development is even more expensive for an aircraft insofar as an aircraft and in particular rotorcraft are generally manufactured in numbers that are small, e.g. in comparison with the numbers of cars that are produced.
Consequently, an aircraft manufacturer tends to envisage making use of other heater systems.
An object of the present invention is to go against that prejudice by proposing an alternative preheater assembly.
In particular, the invention relates to a preheater assembly for an aircraft piston engine, where arranging such a piston engine on an aircraft gives rise to specific difficulties.
Documents FR 2 998 949, DE 39 28 105, FR 1 133 786, BE 402 977, and FR 2 894 724 are known.